The present invention relates generally to single phase electric motors, and in particular to multiple speed capacitor start motors which are switched from the start condition to the run condition by means of a centrifugal switch.
The typical single phase capacitor start motor has a main and auxiliary or start winding wherein the start winding is spatially displaced from the main winding, usually by an angle of ninety electrical degrees. The start winding is connected in series with a start capacitor, which is generally utilized only during starting conditions of the motor. In order to develop starting torque, it is necessary that the currents and the main and start windings be displaced in time phase, and the capacitor, which causes the start phase current to lead the main phase voltage, is utilized for this purpose.
In order to achieve favorable torque characteristics and to prevent damage to the capacitor at full operating speeds of the motor, it is necessary to switch the start capacitor out of the circuit when the rotor has exceeded a predetermined speed. The most widely used device for switching the start capacitor out of the circuit in fractional horsepower motors is the centrifugal switch. This switch comprises a centrifugal device generally mounted on the rotor shaft, and as the rotor increases in rotational speed, centrifugal force actuates a mechanism which causes a collar to move in the axial direction. The collar engages a switch operating arm carrying one or more contacts, and when the arm is moved axially, the contact pairs are opened. This disconnects the start capacitor from the circuit thereby enabling the motor to run at operating speed with its maximum torque and without damage to the capacitor. If desired, the centrifugal switch may also disconnect the start winding from the circuit. Centrifugal switches of the above and other types are available from a wide variety of manufacturers, such as the General Electric Company, Fort Wayne, Ind.
In order to enable the motor to operate at two speeds, it may be provided with two main windings and two auxiliary or start windings, one of each for each speed. In pole-changing motors, the low speed main winding would have a larger pole configuration than the high speed winding, for example, a four-pole winding for a low speed and a two-pole winding for high speed. The start windings would have the same respective pole configurations. Typically, the centrifugal switch for a two-speed motor of this type would have a plurality of contact pairs if the same switch is to be used in both the high speed and low speed configurations.
Two-speed capacitor start motors have been used in a wide variety of applications, such as fan and pump drives. One particular application of such motors which has proved troublesome is in swimming pool filter pumps. Generally, it is believed to be desirable to run these pumps at two speeds, high speed operation being used when activity in the pool is the greatest and more water per unit time is to be filtered, and low speed when the pool is empty and not as much water circulation is necessary.
One of the problems with this type of installation is believed to be that the motor and pump are normally installed in or above the pool deck so that the motor is exposed to the environment. In sandy environments, such as around pools that are located at or near beach areas, blowing sand is believed to be often become lodged between the contacts of the centrifugal switch thereby preventing closure of the contacts during starting of the motor. Because a centrifugal switch is actuated by a mechanical linkage connected between it and the rotor, it is believed to be very difficult to shield the switch from the environment. Although a running seal obtained by providing baffles separating the switch compartment from the rest of the motor has been utilized in the past, it is believed that this has not proven entirely satisfactory and is expensive to manufacture and assemble.
A technique which has been used to protect a single contact pair of a centrifugal switch is to install a rubber boot around it. Although this is satisfactory in motors where the centrifugal switch merely opens a single contact pair, it is believed to be not feasible in the case of two-speed motors of the type in question wherein three contact pairs are spatially separated on the Y-shaped switch operating arm. It is believed that fabricating a boot which would protect all three contact pairs would be expensive to manufacture and difficult to assemble on the motor during manufacturing thereof. The problem to be overcome, then, is to design a two-speed motor which utilizes a single start capacitor and a single centrifugal switch having only one contact pair in both the high speed and low speed configurations. This will enable the use of a single rubber boot enveloping the centrifugal switch single contact pair thereby protecting the same from blowing sand, insects, rain, and other adverse environmental conditions. Additionally, it is desirable that the motor so designed to accommodate a single pole single throw centrifugal switch has the desired range of speed control and is efficient both in operation and from a manufacturing standpoint.
It is, therefore, an object of the present invention to provide a multiple speed single phase motor of the capacitor start variety that utilizes a single centrifugal switch having a common single pole single throw contact pair for both high speed and low speed operation, thereby facilitating booting of the contacts.
It is a further object of the present invention to provide a single phase multiple speed motor of the capacitor start type wherein the speed of the motor can be accurately selected and controlled.
A still further object of the present invention is to provide a single phase multiple speed induction motor of the capacitor start variety wherein the available separation between the low and high speeds is great, and wherein a variety of motors having different speed ratios can be manufactured with the same basic design by varying only the pole configurations.
Another object of the present invention is to provide a single phase multiple speed motor of the capacitor start variety wherein there is an efficient utilization of copper in the main and start windings and wherein the motor will operate efficiently.
Yet another object of the present invention is to provide a capacitor start single phase motor capable of running at at least two different speeds by switching in main and start windings of varying pole configuration.